• Energy Research
• 2021-2025close

This study regards the evaluation of the performance of a thermally stratified tank as an intermediate combi-storage tank for a solar-driven residential thermal system coupled to a seasonal energy storage system. In such applications, the efficient operation of this intermediate tank is crucial to the enhanced exploitation of the harvested solar energy and the minimization of heat losses. In this perspective, the development of a dedicated model in TRNSYS software and its validation with experimental results are investigated. With respect to the simulation model’s discretization, it was found that beyond 60 nodes, the benefits to the model’s accuracy are almost negligible. Comparing the experimental data with the simulation’s results, the predicted temperature profile converges accurately to the measured values under steady-state conditions (threshold stabilization period of 1000 s after charging/discharging has occurred). However, the response of the model deviates considerably under transient conditions due to the lack of detailed inertia modeling of both the tank and the rest of the system components. Conclusively, the developed 1D simulation model is adequate for on- and off-design models where transient phenomena are of reduced importance, whereas for dynamic and semi-dynamic simulations, more detailed models are needed.

This work is partially funded by the Ministerio de Ciencia, Innovación y Universidades de España (RTI2018-093849-B-C31 - MCIU/AEI/FEDER, UE) and the Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (AEI) (RED2018-102431-T). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme. This project has received funding from the European Union´s Horizon 2020 research and innovation programme under the No 764025 (SWS-Heating). Alicia Crespo would also like to acknowledge the financial support of the FI-SDUR grant from the AGAUR of the Generalitat de Catalunya and Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya.

This is the modeling data (input/output files of TOUGHREACT 4.10) used to simulate the reactive transport processes of the Aquifer Thermal Energy Storage (ATES) operations at Stockton University, NJ. Readme.txt lists all the files. TOUGHREACT 4.10 requires to reproduce the modeling output. The modeling data in this submission is related to the Aquifer Injection for Energy Storage purposes outlined in "Reactive Transport Modeling of Aquifer Thermal Energy Storage System at Stockton, NJ During Seasonal Operations".

Deep reinforcement learning (DRL) has demonstrated its effectiveness in the control of energy systems, although it has not yet been applied to sorption thermal energy storage (TES) systems. The operation of sorption TES systems is notably more complicated compared to other TES variants. The discharge of a sorption TES occurs at a particular desorption and evaporation temperature. Achieving a continuous and efficient discharge of a sorption TES is a challenging control task if heat required at the evaporator is obtained from the sun or the environment. Its operation is especially complicated during winter, because of the limited availability of solar irradiation and low ambient temperatures. Thus, this study analyzes for first time in the literature the competitiveness of deep reinforcement learning to control a solar-driven seasonal sorption TES system and compares it against traditional optimized rule-based control strategy. The system, located in Central Europe, supplied domestic hot water and space heating to a single-family house. Two DRL models were developed and trained to operate the system under two different sets of data: 120 winter consecutive days and 60 winter non-consecutive days. The results showed that the DRL control strategy reduced the system operational costs by 28% in a 60 winter days scenario. For a 120 winter days scenario, the operational cost savings decreased to 13% because the smart control performed worst once the sorption TES was fully discharged. These results were derived from a four-year validation data set, bolstering their robustness. The study demonstrates the successful application of DRL in controlling a solar-driven seasonal sorption TES system, yielding considerable economic savings compared to an RBC strategy. Subsequent work will consist of implementing the smart control strategy at prototype level to assess its performance. This work was partially funded by the Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación, Spain (PID2021-123511OB-C31 - MCIN/AEI/10.13039/501100011033/FEDER, EU) and by the Ministerio de Ciencia, Innovación y Universidades, Spain—Agencia Estatal de Investigación (AEI) (RED2018-102431-T). The authors would also like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. Alicia Crespo would also like to acknowledge the financial support of the FI-SDUR grant from the AGAUR of the Generalitat de Catalunya and Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya.

This paper details the use of piece-wise linear regression and non-linear optimisation to determine the heat transfer properties of two ice thermal stores of different volumes (85 m3 and 11 m3). The available energy of each ice storage was determined by the fraction of ice stored in the vessel. The heat loss coefficient was determined using an optimisation algorithm. Using this approach it was possible to determine the heat loss coefficients occurring at different layers of the storage. Validation of the approach yielded a relative mean error of 5.4% and 3.8% for the 85 m3 and 11 m3 storage respectively. This approach is dependent on the measurement of temperature at different segments and the quantity of ice in the storage. It is believed that this approach is scalable and could contribute to a performance database that could provide inputs to energy modelling studies. Journal of Energy Storage, 52 (Part A) ISSN:2352-152X

This article presents a numerical study on the building integration of a liquid sorption storage combined with an air-source electric heat pump. The double staging of the sorption storage (i.e. a chemical heat pump) and an electric heat pump leads to significant electricity demand and CO2 emission reductions. Further, it provides an effective coupling between the heat demand of the building and the electricity supply, allowing for optimal integration of solar energy using photovoltaics. For the buildings analyzed, an autarky level of up to 83% is achieved. Winter electricity demand and emission reductions respectively reached values of up to 41%. The storage integration was studied performing dynamic building simulations. The simulation model for the liquid sorption storage was based on a grey box approach. This features a simple analytical model being tuned to match with performance data available from experiments conducted on a lab scale test rig. The presented integration of a compact seasonal thermal energy storage at the building scale represents a promising approach for a grid compliant integration of renewable energy, significantly reducing electricity demand peaks and related CO2 emissions in winter. Applied Energy, 301 ISSN:0306-2619 ISSN:1872-9118

Chile has set ambitious targets to reach 100% renewable generation in the electric system and supply 80% of its heating with sustainable sources by 2050. The fulfilment of these goals brings new challenges for balancing supply and demand and creates the need for providing the energy networks with operational flexibility from new sources. Thermal energy storage arises as an option that can provide part of this flexibility, decoupling supply and demand by time-shifting power delivery at a competitive cost and with fewer geographical limitations compared to other storage technologies. Although Chilean energy policy has recently turned its attention on these issues, there is still a lack of technical input for assessing the potential of thermal energy storage to support the deployment of renewables in the electric grid and for cleaning heating supply. This thesis aims to bridge that gap and focuses on assessing how different thermal energy storage technologies can help to increase the share of intermittent renewables in the Chilean electric grid and in its residential heating sector. This is performed through techno-economic optimisation of the design and operation of specific thermal energy storage systems configurations. In the case of the electric grid, a linear optimisation model of the Chilean network is developed. The long-term impact of pumped thermal energy storage on the total system’s cost is assessed. Among the main findings, it is concluded that the integration of on-grid 8h capacity storage increases the solar photovoltaic fraction, which leads to reductions in operation and investment costs by 2050. For the residential heating sector, a solar district heating network supported by borehole seasonal thermal storage is proposed as a clean alternative for heating in southern Chile. A simulation-based multi-objective optimisation of the system’s design is performed, focusing on minimising cost and emissions. The results show that this system can be cost-competitive with some conventional heating technologies under specific circumstances. The presence of seasonal thermal storage helps drive down the total emissions by reducing the use of the auxiliary gas heater in winter. Finally, the solar district heating network is combined with a heat pump, and the effect of the power-to-heat scheme supported by short and long-term storage is assessed. It is found that despite the positive impact on cost and emission of the heat pump integration under the proposed configuration, fast charging thermal storage technologies may be better suited to integrate the heat supplied by the heat pump than the slower charging borehole storage. Additionally, by combining the previously developed models, it is established that the flexibility of the electric demand of a heat pump collocated with thermal storage decreases the strain on the electricity system expansion compared with inflexible demand. The findings reported in this thesis set the ground for further research, potentially using more detailed models and assessing other thermal storage technologies to highlight their value and encourage the use of thermal energy storage to assist the Chilean energy transition. Furthermore, these tools and analyses could be applied to other countries and areas following similar energy transition pathways.

Solar heating technology is a promising solution to promote China to achieve the “3060 double carbon” target as soon as possible. And seasonal thermal storage (STS) can effectively solve the mismatch problem of solar heating systems between the supply and demand of thermal energy. Due to the instability of solar radiation resources and heat demand, it is necessary to analyze the dynamic response characteristics of the system. Yet, related studies are still scarce. In this study, a solar heating system with a solar tower receiver and STS was introduced in north China. The dynamic performance of the system is analyzed with a dynamic simulated method in a typical day or typical operation modes, and the switch mechanism between multiple operation modes is also revealed. The impact of different heating strategies on system performance was analyzed. Results showed that the solar fraction of the system reached 89.4% in the third year, which was 3.6% higher than the first year. The quality-quantity heating operation strategies can be effective ways to improve the discharge efficiency of STS and the system performance without any heat pump. The electricity consumption of the pump on the heating side could be significantly reduced by 44.6% compared with the quality control.

Seasonal thermal energy storage is a promising solution for the decarbonization of the heating sector. It can help to overcome the mismatch between heat demand and renewable energy supply and thus reduce emissions of future thermal energy systems. This thesis investigates the techno-economic performance of borehole thermal energy storage (BTES) systems with district heating integration and optional solar collectors. A model is developed to simulate the operation of the BTES and the impact of several design parameters is investigated. For the case study of Furuset, a district of Oslo, the techno-economic performance is assessed for different operational conditions. Key performance indicators are the levelized cost of heat (LCOH), CAPEX, required heat pump size, average outlet temperatures, and emissions. The results implicate that the design parameters impact the performance of the storage system significantly. The mass flow rate within the BTES is a main factor. A mass flow rate that is too high leads to lower outlet temperatures and less heat supplied from the storage, oversizing of the heat pump and thus higher costs and emissions. When the mass flow rate is varied according to the heat demand, the system performance is the best. This case results in a required heat pump capacity of 1.9 MW, average outlet temperatures of 59 °C, CAPEX of 1.7 M€ and LCOH of 141 €/MWh. The emissions considered in this case amount 0.112 kg CO2/kWh, which is 50 % less than if the heat would be supplied by a biogas boiler. Säsongslagring av termisk energi är en lovande lösning för att minska koldioxidutsläppen i uppvärmningssektorn. Det kan bidra till att överbrygga obalansen mellan värmebehovet och förnybar energiförsörjning och därmed minska utsläppen från framtida termiska energisystem. Denna avhandling undersöker den teknisk-ekonomiska prestandan hos system för termisk energilagring i borrhål lagringssystem (BTES) med fjärrvärmeintegration och solfångare som tillval. En modell har utvecklats för att simulera driften av BTES och effekterna av flera designparametrar undersöks. För fallstudien av Furuset, en stadsdel i Oslo, den bedöms den teknisk-ekonomiska prestandan för olika driftförhållanden. Viktiga prestandaindikatorer är den utjämnade värmekostnaden (LCOH), CAPEX, erforderlig värmepumpsstorlek, genomsnittliga utloppstemperaturer och utsläpp. Resultaten tyder på att designparametrarna har en betydande inverkan på lagringssystemets prestanda. Massflödet massflödet inom BTES är en viktig faktor. Ett för högt massflöde leder till lägre utloppstemperaturer och mindre värme från lagret, överdimensionering av värmepumpen och därmed högre kostnader och utsläpp. När massflödet varieras efter värmebehovet är systemets prestanda bäst. Detta fall resulterar en erforderlig värmepumpskapacitet på 1,9 MW, genomsnittliga utloppstemperaturer på 59 °C, CAPEX på 1,7 miljoner euro och LCOH på 141 €/MWh. De utsläpp som beaktas i detta all uppgår till 0,112 kg CO2/kWh, vilket är 50 % mindre än om värmen skulle levereras av en biogaspanna.